Batteries having thin film components are typically manufactured using processing techniques used to fabricate semiconductors or displays. Their small size allows thin film batteries to be used in many applications, such as for example, portable electronics, medical devices, and space systems. The energy density and specific energy of thin film batteries, which express the energy capacity of the battery per unit volume and weight, respectively, are important performance measures, and consequently, it is desirable to increase the energy density and specific energy of such batteries.
The battery components, such as the anode, cathode and electrolyte, can be sensitive to exposure to the surrounding external environment, for example air, oxygen, carbon monoxide, carbon dioxide, nitrogen, moisture and organic solvents. Thus, protective packaging for the battery cell is provided to reduce or eliminate exposure of the thin films to the external environment. For example, a protective sheet of polymer can be laminated onto the battery structure to serve as protective packaging. However, the resultant laminate structure is often much thicker than the original battery. For example, the laminated sheets typically have to be tens or hundreds of micrometers thick to provide adequate protection and structural support, whereas the battery component themselves are only a few micrometers thick. Thus, the laminated packaging substantially increases the weight and volume of the battery, and consequently, reduces its energy density.
A protective covering film deposited onto the battery structure in the same way as the component films of the battery can also serve as protective packaging. Such protective films can include ceramics, metals and parylene. However, such films often do not provide complete protection for a sufficiently long time and can allow gases or other atmospheric elements to leach through the films in a relatively short time of only a few months. These covering films also do not provide adequate structural support, and their use may entail additional packaging to increase the structural strength of the battery, and thus further reduce its energy density. Furthermore, these films have to also be several tens of micrometers thick to provide adequate environmental protection, and this additional thickness further reduces energy density.
A sheet of glass can also be positioned over the battery component films to serve as protective packaging. However, the glass sheet presents an inflexible boundary to the underlying battery component films. For example, the anode typically expands and contracts during the charge and discharge cycles of the battery. The inflexible glass sheet restricts such expansion creating mechanical stresses in the anode which may eventually lead to mechanical or chemical failure and reduce the lifetime or degrade the performance of the battery. The glass sheet is also typically too thick and weighty, thus further reducing the energy density and specific energy of the battery.
Thus, there is a need for a battery that protects against the environmental elements for the battery component films. There is also a need for a battery having relatively high energy density and specific energy. There is further a need for a battery that provides protection to the comprising components for long periods of time. There is also a need for a battery having adequate structural support.